1986 Mercury XR2 150 compression question

[Coon Krazy]

I’m looking at a bass boat.. the exact boat I’ve been looking for. It has a 1986 Mercury XR2 150 on it. The guy says it runs flawlessly. The compression readings he gave me are 110-115 on all 6 with the top 2 cylinders at 110. I’m fully aware that they need to be within 10%. But is them numbers good or bad? How much life does the motor have left at those numbers? Thanks for any help

[wellcraft17]

I have an 86 150 and believe the heads and pistons are the same. Just did a compression test and all six cylinders are 120lbs and have not changed since purchased new in 1985.

[Coon Krazy]

So basically it was 120 new.. so 110-115 isn’t bad at all huh?

[wellcraft17]

If it idles and runs good on top end I think you're good to go. If the compression gets much lower, 105/100, probably looking at rings best case scenario.

[racervboat]

That old motor if not been blown yet is ready for a rebuild or refresh at least pull heads and see what your buying jmo

[CircleHook]

Were carbs held wide open when tested compression? often overlooked when checking compression and it will make 5+ psi difference (up 5)
Pulling heads- frankly I would not allow that on a motor I was selling unless buyer showed up with a set of head gaskets in hand. Head gaskets are $30-50 each plus slight risk of breaking/stripping a bolt.
Do your own compression check for sure- " trust but verify"....... Ronald Reagan I think

[90 5.0]

If they are all that close it’s probubly good, compression gauges can have some variance also and charge of batteri s.

[Chad Phillips]

I checked mine the other day and it was 130 across all 6. Doesn't look like it's ever been into. Whole rig is clean original(17' Bullet)

[j_martin]

Gauges vary, throttle open or closed has an effect, so does weather, ie high or low atmospheric pressure. If compression is fairly even,and if it idles good, odds are it's OK.

You are buying a used motor, after all.

[W2F a V-King]

If they are all that close it’s probubly good, compression gauges can have some variance also and charge of batteri s.

This ^^ and if you really want to see what "Life" is left....do a leak down test. Gives a good indication of cylinder pressure leaks/leakage = ring sealing ability.(if no abnormal leaks are present, yours seems OK given they are all within a few lbs. of each other)
Spin it fast and on a warm motor.

Also like mentioned above, pulling the heads for a look see, will give you satisfaction of knowing what your cylinders/piston tops look like.
And a new set of gaskets are relatively cheap for a set. Might have the heads Shaved a bit while their off for a bit of added ponies across the rpm range, but CC them first.

A USB powered bore scope is cheaper yet and can give you a look see inside through the spark plug hole... < $15 and plugs into your smart phone.

The old 2.0 L motors are almost bullet proof.

Welcome to S&F...Best Boating Forum on the planet !!

[Glastron1987]

If you're compression testing a motor that hasn't been run in a while so the carbs could be gummy, is it necessary to drain them out or can you get away with just squirting a little fogger in the cylinders to make sure they are not dry so that there no damage caused?

[FMP]

Fogger will raise your number, more important is why the carbs weren't drained prior to the long storage.